The Magicshine PMJ-828 heavy duty battery pack features a backlit display indicating battery capacity. The battery shell contains four 18650 rechargeable lithium batteries in a waterproof casing. Battery is mounted to bike frame with a velcro strap for easy on, easy off placement. Display illuminates at a touch, showing battery life and voltage. Charging time is 3-3.5 hours using the standard Magicshine charger.